CB400f with K&N Pods Filters - what carb jetting are you using ?

[400 Cafe Racer]

I think there are a number of members who are running with K&N pod air filters on the 400f and I wondered what options users have found on Idle and Main jet sizes.

Dennis

[Norniron]

85 mains and 42 pilots

[400 Cafe Racer]

Hi Norniron,

Thanks for your reply.

I  recently purchased my 400f and did a full engine strip and inspection to check clearances and timing chain components. I did not take too much notice of  its before the rebuild.

It is set up with 95 Mains and 35 Pilots but I feel there is some further scope for fine tuning to smoothen things out more. It is fitted with a "Shorty" silencer.

Can you say how yours performs through the range from idle to top end and what the plug colours are like with the 85 Mains and 42 pilots.

Thanks

Dennis

[Norniron]

Hi Dennis,there are flat spots,but thats pods for you.
Plug colour is fine.
Obviously best set up is stock

[400 Cafe Racer]

Hi Norniron,
Thanks for your useful feedback.

I have my carbs on the bench for inspection at the moment due to excessive richness on carb 1. My post on Idle Air Screws will show the details.

The PO fitted a Innovate Motorsports exhaust Air/Fuel ratio analyser so when I have things up and running properly it should provide some readings of interest.

Cheers

Dennis

[400 Cafe Racer]

Hi Dennis,there are flat spots,but thats pods for you.
Plug colour is fine.
Obviously best set up is stock

Hi Norniron,
Which needle notch did you find worked best on your set up please.

Cheers

Dennis

[Norniron]

Hi Dennis,there are flat spots,but thats pods for you.
Plug colour is fine.
Obviously best set up is stock

Hi Norniron,
Which needle notch did you find worked best on your set up please.

Cheers

Hi Dennis,its still in the middle notch

Dennis

[400 Cafe Racer]

Hi Norniron,

Thanks for your reply. I am currently doing some tests on different positions and different jet settings using the A/F meter (Air Fuel ratio measurement) under live running conditions.

As you can appreciate, every change of needle position or jet means, seat, tank and carbs all have to be removed and carbs stripped to make the changes. Then on refitting etc carbs all need to be re-syncronised and adjusted. Not a quick job , but it is worth it.

1. I initially tried the carbs as the PO had them set, just checking and correcting float levels and correcing the dynamic timing when I rebuilt the engine. The outcome was reasonable torque and power, but mixture generally smelling too rich, some smelling in the oil and readings of about 9.8 :1 and 10.2 :1 throughout the range and some plug fouling occasionally. Clearly far too rich. 

2. Next test.  Change main jet from 95 to 85. Result was good torque and power, with 12 :1 AFR on full throttle and between 10.9 to 11.2 :1 on 1/4 to 3/4 throttle. Still a tad too rich.

3. Previously set on one slot lower/richer than normal, I decided to try the middle notch setting and in testing found it slightly erratic reading between 13.1 :1 and 14 :1 on all openings between 1/4 and 3/4 throttle. I found the engine a little less smooth on acceleration, with a drop in torque and power, plus an increase of approx 10 degrees  in engine running/oil temperature. Not happy with this setting, but made a valuable discovery while setting the needles lower. I think the erratic reading and less smoothness were pre-ignition, which also affected engine temperature.

I started with No1 carb going to the centre notch, then 2 &3  BUT when I got to No4 I had slight difficulty getting the assembly apart to gain access to the needle.
The reason was that the needle and clip were fitted ABOVE the clamping plate, instead of beneath it in the recessed portion for the clip.
This meant that this carb needle was the equivalent of about 3 to 4 notches too rich.

4. The next test will be with the needles 1 notch lower (richer) than standard where the best torque and power were found, as on test 2. With the needle in No4 carb now seated correctly this should address the previous slight overall richness. Ideally I am looking to set up for between 11.8 and 12.7 where the best power with cooler running should be. This will not give best consumption but will be kinder on the pistons.
Due to working on front forks it will be a few  days before I re-test.
 
Cheers

Dennis

[Laverdaroo]

Super interesting that, keep us posted on next setting results please. I have a Steeldragon air box coming from the states and although not the same, its sill not a standard thing so any info gleaned from your posts is very useful, and potentially a good starting point for me.

[400 Cafe Racer]

Super interesting that, keep us posted on next setting results please. I have a Steeldragon air box coming from the states and although not the same, its sill not a standard thing so any info gleaned from your posts is very useful, and potentially a good starting point for me.

Hi Laverdaroo,

Got around to doing the final Carb settings today.

Recap:  K&N Pods. fitted to  Standard Carbs.
New jetting to - Idle 40, with mixture screw 1.75 turns out on all Carbs.
Main jet 85
Needle position in slide Clip Lowered by one notch from middle, ie 1 notch richer

The results are giving AFRatio readings of between 11.7 and 12.4, which is just where I needed them to give best power, torque and cooler running.

I am well pleased after investing the time in the multiple "strip and reset" project on the carbs and these will remain my final settings.

I hope this post may prove helpful to other members.

Cheers

Dennis

[Laverdaroo]

Wicked, thanks for the info that’s a great place to start. I’m restricted to a good old colour tune here those settings will accelerate the progress no end, parson the pun

Cheers for that.


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[zombie365]

Ayup Dennis

Thanks for sharing your settings , I'm going to be using them for my bike. I have K&N with Delkavik exhaust. Currently my build has standard jets 75 40 and notch is in middle , bike is bogging down with full throttle. Hopefully your settings will be good for me as well!

Just wanted to clarify that I've adjusted the needles correcty? See pictures below . Top is original, bottom is new needle with one notch down. Is that correct?

Thanks again bud !

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[Oddjob]

Depends on whether the bogging down is caused by weak or rich mixture. If rich then no, if weak then yes.

[400 Cafe Racer]

Ayup Dennis

Thanks for sharing your settings , I'm going to be using them for my bike. I have K&N with Delkavik exhaust. Currently my build has standard jets 75 40 and notch is in middle , bike is bogging down with full throttle. Hopefully your settings will be good for me as well!

Just wanted to clarify that I've adjusted the needles correcty? See pictures below . Top is original, bottom is new needle with one notch down. Is that correct?

Thanks again bud !

(Attachment Link)

Hi zombie365,

Thats good timing I think.  It just so happens that I decided to change my "Shorty" silencer late last year because it was a bit too obtrusive at full throttle. My choice was the Delkevic. A nice tonal balance and road legal.

Your needle clips is in the same position as mine ie one below centre.

You will see from my previous tests the Air/Fuel ratios which were recorded.

What I have found since fitting the Delkevic is that it bogs down slightly when pullling out of roundabouts or sometimes when pulling away from traffic lights.  The Air/Fuel ratio at say just above idle to 1/4 throttle has now gone significantly richer at 9.8:1 far too much for clean combustion.

I haven't got around to the carbs strip and change yet, but my plan is to go for the 35 pilot jet to lean out the small throttle/intermediate opening and set the mixture screw to give around 13:1 for a clean idle. After this it will be down to road test and results. Due to shortage of time at the moment I am unlikely to be able to get back to it until late May - June. Check that your float levels are equal and true. Also that centrifugal advance system is working correctly on timing, to give correct full advance when checked with a strobe light. Retarded ignition will raise heat and reduce power.

I would say that for me, the other Jet and needle settings I made still retained the good power and torque results, pulling strongly in 6th gear, with the Delkevic fitted.

Let us know how you get on when you have set up and tested.

Hope this help you,

Cheers Dennis

[zombie365]

Thanks for the info Dennis.

I'm going to be rebuilding my carbs tomorrow, currently they're stripped down ready to be ultrasonically cleaned.

I've ordered some #35 slow jets as per your recommendation. 

I will build them back up with the following:

-Needle cir-clip 1 notch down from middle.
-35 slow
-85 main

I don't have AFR Meter, what would you recommend setting the mixture screw to?

Cheers,

Sam